What is the spreading of particles from a crowded area to a less crowded area called?

1. Particles in liquids and gases keep moving in unpredictable directions. 2. This random movement carries them from where they are crowded to where they are not. 3. Spreading out in this way is called diffusion, and it is why smells travel. _Source: Siyavula Natural Sciences Grade 8 (CC BY 4.0), Random movement of particles_